If you don't know somebody's parents names use the old Irish Catholic custom of naming children viz:First born male child named after the father’s fatherFirst born female child named after the father’s motherSecond born male child named after the mother’s fatherSecond born female child named after the mother’s motherThird born male child named after fatherThird born female child named after mother and so on.It does not always run true but it can be a very good guide for investigating further possibilities.